Threaded tubular connection

Abstract

Threaded tubular interference fit interconnections and related production techniques are disclosed that are for example useful with large diameter tubular members, including pipe bodies, that can for example function as casing for oil, gas, geothermal, disposal and other wells. In a preferred aspect of the invention there is root-to-crest and/or flank-to-flank interference between nose and inner portions of male and female threads of the disclosed interconnections, such as substantially to seal them against leakage at the maximum internal and/or external pressure rating of the pipe body, and a run-out portion of the male thread and a corresponding portion of the female thread engage one another with interference to retain threaded engagement between said run-out and corresponding portions at the maximum axial force rating of the pipe body and also at the maximum internal and/or external pressure rating of the pipe body. These connections, when applied to API line pipe or other tubular products, can allow them to properly function as large diameter casing exhibiting easy and economical manufacture with existing machinery, easy installation in the field, good balance between geometric and load capacity transparency, and freedom from some undesirable characteristics of prior products.

I claim: 
     
       1. In combination, a length of threaded pipe comprising a pipe body, a male thread with a run-out portion and regular turns having load flank, stab flank, crest and root, and a female member with female thread to enable coupling of said pipe to a further length of said threaded pipe to form a threaded connection, said combination comprising: A. said male thread being tapered over at least a portion of its axial length, including a nose portion thereof,   B. said female thread being tapered over at least a portion of its axial length, including an inner portion thereof which threadably engages with said nose portion when said threads are in made-up position,   C. said male and female threads having load flank angles and thread heights sufficient to ensure that with the threads in made-up position in the threaded connection, at least the load flank of the male thread of said connection will remain engaged with the load flank of the female thread of said connection, even in response to an axial load on said connection substantially corresponding to the axial yield strength of the pipe body;   D. said male and female threads being so dimensioned in relation to each other at said nose and inner portions to ensure that in made-up position in said connection a root-to-crest and/or flank-to-flank interference fit will exist between said nose and inner portions, said interference being sufficiently large for forming in the threads, with the aid of thread compound present in gaps which may optionally exist between said male and female threads, a seal that substantially prevents leakage of fluid through the threads 1. when the connection is subjected to internal fluid pressure corresponding to the internal pressure rating of the pipe body; or   2. when the connection is subjected to external fluid pressure corresponding to the external pressure rating of the pipe body; and     E. said male and female threads being so dimensioned in relation to each other that in made-up position in said connection the run-out portion of the male thread will engage a corresponding portion of the female thread in an interference fit, said interference being sufficient to retain threaded engagement between said run-out and corresponding portions 1. when the connection is subjected to axial tension corresponding to the axial yield strength of the pipe body and to internal fluid pressure corresponding to the internal pressure rating of the pipe body, or   2. when the connection is subjected to axial tension corresponding to the axial yield strength of the pipe body and to external fluid pressure corresponding to the external pressure rating of the pipe body,     and said interference being less than that which will cause either substantial destructive hoop stress yield deformation of said pipe or female member or substantial destructive galling of said male or female threads.   
     
     
       2. Apparatus according to claim 1 wherein the interference between said nose and inner portions is sufficiently large for substantially preventing leakage of fluid through the threads when the connection is subjected to internal fluid pressure corresponding to the internal pressure rating of the pipe body. 
     
     
       3. Apparatus according to claim 1 wherein the interference between said nose and inner portions is sufficiently large for substantially preventing leakage of fluid through the threads when the connection is subjected to external fluid pressure corresponding to the external pressure rating of the pipe body. 
     
     
       4. Apparatus according to claim 1 wherein the interference between said nose and inner portions is sufficiently large for substantially preventing leakage of fluid through the threads A. when the connection is subjected to internal fluid pressure corresponding to the internal pressure rating of the pipe body, and   B. when the connection is subjected to external fluid pressure corresponding to the external pressure rating of the pipe body.   
     
     
       5. Apparatus according to claim 1 wherein the interference between the run-out portion of the male thread and the corresponding portion of the female thread is sufficient to retain threaded engagement between said run-out and corresponding portions when the connection is subjected to axial tension corresponding to the axial yield strength of the pipe body and to internal fluid pressure corresponding to the internal pressure rating of the pipe body. 
     
     
       6. Apparatus according to claim 1 wherein the interference between the run-out portion of the male thread and the corresponding portion of the female thread is sufficient to retain threaded engagement between said run-out and corresponding portions when the connection is subjected to axial tension corresponding to the axial yield strength of the pipe body and to external fluid pressure corresponding to the external pressure rating of the pipe body. 
     
     
       7. Apparatus according to claim 1 wherein the interference between the run-out portion of the male thread and the corresponding portion of the female thread is sufficient to retain threaded engagement between said run-out and corresponding portions A. when the connection is subjected to axial tension corresponding to the axial yield strength of the pipe body and to internal fluid pressure corresponding to the internal pressure rating of the pipe body, and   B. when the connection is subjected to axial tension corresponding to the axial yield strength of the pipe body and to external fluid pressure corresponding to the external pressure rating of the pipe body.   
     
     
       8. Apparatus according to claim 1 wherein A. the interference between said nose and inner portions is sufficiently large for substantially preventing leakage of fluid through the threads when the connection is subjected to internal fluid pressure corresponding to the internal pressure rating of the pipe body, and   B. the interference between the run-out portion of the male thread and the corresponding portion of the female thread is sufficient to retain threaded engagement between said run-out and corresponding portions when the connection is subjected to axial tension corresponding to the axial yield strength of the pipe body and to internal fluid pressure corresponding to the internal pressure rating of the pipe body.   
     
     
       9. Apparatus according to claim 1 wherein A. the interference between said nose and inner portions is sufficiently large for substantially preventing leakage of fluid through the threads when the connection is subjected to internal fluid pressure corresponding to the internal pressure rating of the pipe body, and   B. the interference between the run-out portion of the male thread and the corresponding portion of the female thread is sufficient to retain threaded engagement between said run-out and corresponding portions when the connection is subjected to axial tension corresponding to the axial yield strength of the pipe body and to external fluid pressure corresponding to the external pressure rating of the pipe body.   
     
     
       10. Apparatus according to claim 1 wherein A. the interference between said nose and inner portions is sufficiently large for substantially preventing leakage of fluid through the threads when the connection is subjected to external fluid pressure corresponding to the external pressure rating of the pipe body, and   B. the interference between the run-out portion of the male thread and the corresponding portion of the female thread is sufficient to retain threaded engagement between said run-out and corresponding portions when the connection is subjected to axial tension corresponding to the axial yield strength of the pipe body and to internal fluid pressure corresponding to the internal pressure rating of the pipe body.   
     
     
       11. Apparatus according to claim 1 wherein A. the interference between said nose and inner portions is sufficiently large for substantially preventing leakage of fluid through the threads when the connection is subjected to external fluid pressure corresponding to the external pressure rating of the pipe body, and   B. the interference between the run-out portion of the male thread and the corresponding portion of the female thread is sufficient to retain threaded engagement between said run-out and corresponding portions when the connection is subjected to axial tension corresponding to the axial yield strength of the pipe body and to external fluid pressure corresponding to the external pressure rating of the pipe body.   
     
     
       12. Apparatus according to claim 1 wherein A. the interference between said nose and inner portions is sufficiently large for substantially preventing leakage of fluid through the threads 1. when the connection is subjected to internal fluid pressure corresponding to the internal pressure rating of the pipe body, and     
     
     
       2. when the connection is subjected to external fluid pressure corresponding to the external pressure rating of the pipe body, and B. the interference between the run-out portion of the male thread and the corresponding portion of the female thread is sufficient to retain threaded engagement between said run-out and corresponding portions 1. when the connection is subjected to axial tension corresponding to the axial yield strength of the pipe body and to internal fluid pressure corresponding to the internal pressure rating of the pipe body, and   2. when the connection is subjected to axial tension corresponding to the axial yield strength of the pipe body and to external fluid pressure corresponding to the external pressure rating of the pipe body.     
     
     
       13. Apparatus according to claim 12 wherein said male thread is formed adjacent at least one end of said pipe and said male thread and female thread are so dimensioned in relation to each other, in both thread profile and diameter, A. to provide between them flank to flank gaps and a root to crest gap at the major diameter of the threads and   B. to ensure that a root to crest interference fit will exist between them in made-up position at the minor diameter of the threads,   C. said interference being sufficiently large and said gaps being sufficiently small, at the nose portion of said male thread, 1. to provide said seal, and   2. to cause the interference between the threads to gradually decrease along the axial length of the threads in a direction away from said at least one end.     
     
     
       14. Apparatus according to claim 1 wherein A. said male thread is a single step, single lead thread of substantially constant lead of at least about 0.2 inch having a substantially uniform single taper formed about a central axis with substantial portions of the axial length of its root and crest being rectilinear and parallel to said axis, said male thread being formed adjacent at least one end of said pipe and including a nose portion composed of up to about half of said regular thread turns nearest said at least one end, and   B. said female thread is a single step, single lead thread of substantially constant lead of at least about 0.2 inch having a substantially uniform single taper formed about a central axis with substantial portions of the axial length of its root and crest being rectilinear and parallel to said axis, and including an inner portion composed of female thread turns which threadably engage with the nose portion of the male thread when said threads are in made-up position.   
     
     
       15. Apparatus according to claim 1, 12 or 14 wherein said male thread and female thread are dimensioned in relation to each other, in both thread profile and diameter, to provide a root to crest or flank to flank gap between them and to ensure that a root to crest or flank to flank interference fit will exist between them in said connection. 
     
     
       16. Apparatus according to claim 14 wherein said male thread is formed adjacent at least one end of said pipe and said male thread and female thread are so dimensioned in relation to each other, in both thread profile and diameter, A. to provide between them flank to flank gaps and a root to crest gap at the major diameter of the threads and   B. to ensure that a root to crest interference fit will exist between them in made-up position at the minor diameter of the threads,   C. said interference being sufficiently large and said gaps being sufficiently small, at the nose portion of said male thread, 1. to provide said seal, and   2. to cause the interference between the threads to gradually decrease along the axial length of the threads in a direction away from said at least one end.     
     
     
       17. Apparatus according to claim 1, 12, 14, 18, 19, 20, 13 or 16 wherein A. said male thread has a hook profile and is tapered over at least a nose portion of its axial length,   B. said female thread has a hook profile which is matingly compatible with the male thread profile and is tapered over an inner portion of its axial length which will threadably engage with the nose portion of said male thread in made up position in said connection,   C. at least one of said threads has its surface roughened in an irregular manner to assist in retention of a thread compound in place at the surface thereof, and   D. said male and female threads are so dimensioned in relation to each other 1. to provide a root to crest or flank to flank gap between them and   2. to ensure that a root to crest or flank to flank interference fit will exist between them in made up position,   3. said interference being sufficiently large and said gap being sufficiently small to substantially prevent, with the aid of thread compound therein and without substantial destructive galling of the threads, leakage through the nose and inner portions thereof when the connection is subjected to said fluid pressure and to axial tension corresponding to the axial yield strength of the pipe body.     
     
     
       18. Apparatus according to claim 1 wherein said male thread and female thread are so dimensioned in relation to each other, in both thread profile and diameter, to provide between them flank to flank gaps and a root to crest gap at the major diameter of the threads and to ensure that a root to crest interference fit will exist between them in made-up position at the minor diameter of the threads. 
     
     
       19. Apparatus according to claim 1 wherein said male thread is formed adjacent at least one end of said pipe and said male thread and female thread are so dimensioned in relation to each other, to cause the interference between them to gradually decrease along the axial length of the threads in a direction away from said at least one end. 
     
     
       20. Apparatus according to claim 1 wherein said male thread is formed adjacent at least one end of said pipe and said male thread and female thread are so dimensioned in relation to each other, in both thread profile and diameter, A. to provide between them flank to flank gaps and a root to crest gap at the major diameter of the threads and   B. to ensure that a root to crest interference fit will exist between them in made-up position at the minor diameter of the threads,   C. said interference being sufficiently large and said gaps being sufficiently small, at the nose portion of said male thread, 1. to provide said seal, and   2. to cause the interference between the threads to gradually decrease along the axial length of the threads in a direction away from said at least one end.     
     
     
       21. Apparatus according to claim 1, 14 or 20 wherein at least one of said threads has its surface roughened in an irregular manner to assist in retention of a thread compound in place at the surface thereof. 
     
     
       22. In combination, a length of threaded pipe comprising a pipe body with male thread turns having load flanks, stab flanks, crests and roots and a female threaded member for coupling of said pipe to a further length of threaded pipe to form a threaded connection, said combination comprising: A. said male thread having a hook profile and being tapered over at least a nose portion of its axial length,   B. said female thread having a hook profile matingly compatible with the male thread profile and being tapered over an inner portion of its axial length which will threadably engage with the nose portion of said male thread in made up position,   C. at least one of said threads having its surface roughened in an irregular manner to assist in retention of a thread compound in place at the surface thereof, and   D. said male and female threads being so dimensioned in relation to each other   
     
     
       1. to provide a root to crest or flank to flank gap between them and 2. to ensure that a root to crest or flank to flank interference fit will exist between them in made up position,   3. said interference being sufficiently large and said gap being sufficiently small to substantially prevent, with the aid of thread compound therein and without substantial destructive galling of the threads, leakage through the nose and inner portions thereof a. when the connection is subjected to internal fluid pressure corresponding to the internal pressure rating of the pipe body and to axial tension corresponding to the axial yield strength of the pipe body, or   b. when the connection is subjected to external fluid pressure corresponding to the external pressure rating of the pipe body and to axial tension corresponding to the axial yield strength of the pipe body.     
     
     
       23. Apparatus according to claim 1, 14, 20 or 22 in which the male and female threads are substantially uniformly tapered at least in the nose and inner portions thereof. 
     
     
       24. Apparatus according to claim 1, 14, 20 or 22 in which the male and female threads are substantially uniformly tapered over at least a major portion of their respective axial lengths to form included first and second apex angles of taper. 
     
     
       25. Apparatus according to claim 1, 14, 20 or 22 in which the male and female threads are each substantially uniformly tapered substantially throughout at least the mutually engaging portions of their respective axial lengths to form included first and second apex angles of taper. 
     
     
       26. Apparatus according to claim 1, 14, 20 or 22 in which the male and female threads, in made-up position, have radial root to crest interference substantially throughout at least about half of the axial length of their mutually engaging portions. 
     
     
       27. Apparatus according to claim 1, 14, 20 or 22 in which the male and female threads, in made-up position, have radial root to crest interference substantially throughout the axial length of their mutually engaging portions. 
     
     
       28. Apparatus according to claim 1, 14, 20 or 22 in which the male and female threads, as viewed in longitudinal cross-section, have negatively inclined load flanks and positively inclined stab flanks. 
     
     
       29. Apparatus according to claim 1, 14, 20 or 22 in which the male and female threads have crests and roots, as viewed in longitudinal cross-section, that include rectilinear bearing surfaces of substantial length in the axial direction. 
     
     
       30. Apparatus according to claim 29 in which the male and female threads, as viewed in longitudinal cross-section, have negatively inclined load flanks and positively inclined stab flanks. 
     
     
       31. Apparatus according to claim 29 in which the male thread has major and minor diameters with which the male thread crest and root respectively coincide, and root to crest interference is provided at at least one of said diameters. 
     
     
       32. Apparatus according to claim 29 in which the male thread has major and minor diameters with which the male thread crest and root respectively coincide, and root to crest interference is provided at the minor diameter. 
     
     
       33. Apparatus according to claim 32 in which there is a small clearance between the male thread crest and the female thread root at the major diameter. 
     
     
       34. Apparatus according to claim 1, 14, 20 or 22 wherein the male thread has a run-out portion that includes run-out thread turns. 
     
     
       35. Apparatus according to claim 34 wherein at least a portion of the run-out thread turns have a crest which has been machined to a common diameter with an adjacent unthreaded portion of the pipe wall, which unthreaded portion is of reduced diameter relative to portions of the pipe wall not so machined. 
     
     
       36. Apparatus according to claim 34 wherein the female member includes wall means and the run-out thread turns are present in a longitudinal distance interval of the pipe wall which is of restricted length, for retaining such thread turns substantially completely within the wall means when the threads are in made-up position. 
     
     
       37. Apparatus according to claim 34 wherein female thread turns have their crests bottomed in the root of substantially all of the male run-out thread turns, when the threads are in made-up position. 
     
     
       38. Apparatus according to claim 34 wherein the female member includes wall means, at least a portion of the run-out thread turns have crests which have been machined to a common diameter with an adjacent unthreaded portion of the pipe wall, which unthreaded portion is of reduced diameter relative to portions of the pipe wall not so machined, the longitudinal distance interval within which the run-out thread turns are present in the pipe wall is restricted for retaining such thread turns substantially completely within the wall means of the female member when the threads are in made-up position, and the female thread is positioned for causing substantially all of the run-out thread turns to be threadedly engaged by female thread turns which have their crest bottomed in the root of the run-out thread turns with the threads in made-up position. 
     
     
       39. Apparatus according to claim 1, 14, 20 or 22 wherein the female member includes wall means having an unthreaded cylindrical inner surface adjacent an open end of the female member. 
     
     
       40. Apparatus according to claim 39 wherein the male thread turns present on the pipe include both regular thread turns and run-out thread turns, and the female member has wall means including at least one female thread turn adjacent said inner surface, which thread turn will not threadedly engage any of said run-out thread turns when the threads are in made-up position. 
     
     
       41. Apparatus according to claim 40 wherein at least a portion of the run-out thread turns have a crest which has been machined to a common diameter with an adjacent unthreaded portion of the pipe wall which is of reduced diameter relative to portions of the pipe wall not so machined, and the female thread turns which will not threadedly engage the run-out thread turns will be closely adjacent or in abutting relationship to said pipe wall portion of reduced diameter, when the threads are in made-up position. 
     
     
       42. Apparatus according to claim 1, 14, 20 or 22 wherein the female member has wall means with an open end, the male and female threads are tapered along their axial lengths to form first and second apex angles of taper respectively, said second angle being greater than the first, and the difference between said first and second apex angles is an amount in the range of about 0.01 to about 1 degrees which is sufficient for producing in the wall means at its open end a hoop stress that is lower than the hoop stress in the region of the wall means surrounding the inner portion of the female thread. 
     
     
       43. Apparatus according to claim 42 wherein the difference between said angles is in the range of about 0.05 to about 0.7 degrees. 
     
     
       44. Apparatus according to claim 42 wherein the difference between said angles is in the range of about 0.1 to about 0.4 degrees. 
     
     
       45. Apparatus according to claim 1, 14, 20 or 22 wherein the female member has wall means with an open end, the male thread turns present in the pipe wall include both regular thread turns and run-out thread turns, at least a portion of the run-out thread turns have a crest which has been machined to a common diameter with an adjacent unthreaded portion of the pipe wall which is of reduced diameter relative to portions of the pipe wall not so machined, the male and female threads are tapered along their axial lengths to form first and second apex angles of taper respectively, said second angle being greater than the first, and the difference between said first and second apex angles is an amount in the range of about 0.01 to about 1 degrees which is sufficient for producing in the wall means at its open end a hoop stress that is lower than the hoop stress in the region of the wall means surrounding the inner portion of the female thread. 
     
     
       46. Apparatus according to claim 1, 14, 20 or 22 wherein the pipe conforms substantially to the strength requirements of API Line Pipe Specification 5L, as amended on May 31, 1988. 
     
     
       47. Apparatus according to claim 1, 14, 20 or 22 wherein the pipe has said male thread formed in a first end thereof, the female member has wall means which is an integral portion of a second end of the pipe wall and the female thread is formed in a portion said second end. 
     
     
       48. Apparatus according to claim 1, 14, 20 or 22 wherein said male threads are present at both a first and a second end of the pipe wall, and the female member is a coupling that is not an integral portion of the pipe wall and has two open ends and two sets of said female threads therein. 
     
     
       49. Apparatus according to claim 48 wherein the coupling is formed of material that conforms substantially to the strength requirements of section 8 of API Coupling Stock Standard 5CT, as amended on Mar. 15, 1988. 
     
     
       50. Apparatus according to claim 1, 14, 20 or 22 wherein the pipe and/or female member have a thread or threads formed of A. steel that contains one or more grain refiners in amounts sufficient to provide the steel with a microstructure substantially finer than that of API Casing, or   B. metal characterized by carbon and sulfur contents substantially below those of API Casing and having a substantial tendency to gall destructively when fully made up in a leak-resistant, interference fit threaded joint, or   C. non-ferrous metal having a substantial tendency to gall destructively when fully made up in a leak-resistant, interference fit threaded joint, or   D. a combination of the foregoing.   
     
     
       51. Apparatus according to claim 1, 14, 20 or 22 wherein the pipe and/or female member have at least one thread formed of an alloy composed substantially of at least one metal selected from among nickel, titanium and aluminum. 
     
     
       52. Apparatus according to claim 1, 14, 20 or 22 wherein the pipe and/or female member have walls and threads formed at least in part of polymeric material. 
     
     
       53. Apparatus according to claim 52 wherein the polymeric material includes material selected from among epoxy, polyester, polyether, acetal and polyphenylene sulfide polymers. 
     
     
       54. Apparatus according to claim 52 wherein the polymeric material is reinforced with fiber. 
     
     
       55. Apparatus according to claim 1, 14, 20 or 22 wherein at least the male thread has its surface roughened in an irregular manner to promote adherence of a layer of thread compound to said surfaces. 
     
     
       56. Apparatus according to claim 1, 14, 20 or 22 wherein at least one of said threads has its surface roughened in an irregular manner to assist in retention of a thread compound in place at the surface thereof and the roughened surface comprises rugae formed by applying to the surface a coating comprising at least one phosphate selected from among manganese phosphate and zinc phosphate. 
     
     
       57. Apparatus according to claim 1, 14, 20 or 22 wherein at least one of said threads has its surface roughened in an irregular manner to assist in retention of a thread compound in place at the surface thereof and the roughened surface comprises roughness formed by an etchant. 
     
     
       58. Apparatus according to claim 1, 14, 20 or 22 wherein at least one of said threads has its surface roughened in an irregular manner to assist in retention of a thread compound in place at the surface thereof and the roughened surface comprises surface irregularities formed by blasting the surfaces with particulate material. 
     
     
       59. Apparatus according to claim 58 wherein the amount of blasting with particulate material is sufficient to conform said surfaces to the National Association of Corrosion Engineers (Houston, Tex., U.S.A.) Standard TM 0170-70, white metal visual standard NACE No. 1. 
     
     
       60. Apparatus according to claim 1, 14, 20 or 22 having in or on the surfaces of the female thread at least one material in solid form for enhancing the galling resistance of said surfaces. 
     
     
       61. Apparatus according to claim 60 wherein said materials include at least one metal from the group including zinc, manganese, copper, tin, nickel and silicon. 
     
     
       62. Apparatus according to claim 60 wherein said materials include at least one phosphate selected from among manganese phosphate and zinc phosphate. 
     
     
       63. Apparatus according to claim 60 wherein said materials include an electroplated layer of at least one metal from the group including nickel, zinc, tin and copper. 
     
     
       64. Apparatus according to claim 60 wherein said materials include a layer of electroless nickel plate. 
     
     
       65. Apparatus according to claim 60 wherein said material includes an implant comprising at least one metal from the group including silicon, chromium, and the noble metals in said thread surfaces. 
     
     
       66. Apparatus according to claim 1, 14, 20 or 22 wherein the surface of the male thread has been roughened in an irregular manner for promoting adherence of a layer of thread compound to said surface and the surface of the female thread includes at least one implanted or coating material in solid form for enhancing the galling resistance of said surface. 
     
     
       67. Apparatus according to claim 66 wherein the surface of the male thread has been roughened by blasting or etching and said implanted or coating material includes at least one phosphate selected from among manganese phosphate and zinc phosphate at the surface of the female thread. 
     
     
       68. Apparatus according to claim 1, 14, 20 or 22 wherein the interference fit in at least the nose and inner portions is characterized by the male and female threads having predetermined bearing diameters, and by the male thread having a bearing diameter, in an unstressed condition, which exceeds the bearing diameter of the female thread, in an unstressed condition, by a ratio in the range of about 0.0005 to about 0.005 inches of such excess per inch of said female thread bearing diameter. 
     
     
       69. Apparatus according to claim 68 wherein the pipe and female member threads are of metallic material and said ratio is in the range of about 0.001 to about 0.005 inches per inch. 
     
     
       70. Apparatus according to claim 68 wherein said ratio is in the range of about 0.0015 to about 0.0025 inches per inch. 
     
     
       71. Apparatus according to claim 68 wherein the interference is sufficient to impart substantial leak resistance to the threaded connection when thread compound is present in the clearance. 
     
     
       72. Apparatus according to claim 68 in which the male thread has major and minor diameters with which the male thread crest and root respectively coincide, and root to crest interference is provided between the male and female threads at the minor diameter. 
     
     
       73. Apparatus according to claim 72 in which there is a small clearance between the male thread crest and the female thread root at the major diameter. 
     
     
       74. Apparatus according to claim 1, 14, 20 or 22 wherein the diameter of the pipe is at least about 12 inches. 
     
     
       75. Apparatus according to claim 1, 14, 20 or 22 wherein the diameter of the pipe is in the range of about 12 to about 60 inches. 
     
     
       76. Apparatus according to claim 1, 14, 20 or 22 wherein the diameter of the pipe is in the range of about 12 to about 30 inches. 
     
     
       77. Apparatus according to claim 1, 14, 20 or 22 wherein the diameter of the pipe is in the range of about 13 and 5/8 to about 20 inches in diameter, with wall thickness in the range of about 0.4 to 0.8 inches.